1. Field of the Invention
The present invention pertains to the filtration of gas streams to remove contaminants therefrom, particularly pathogens.
2. Background Art
Filtration of gas streams, particularly air streams, is a well developed technology. In the home, for example, a variety of filters, including electrostatic precipitators, are used to remove dust, microorganisms, and particulates from forced air HVAC systems. Such systems still allow large numbers of particulates to be circulated in the air stream, however, and in more stringent environments, including chemical and biological laboratories, hospitals, chemical plants, and the like, large surface area, e.g. pleated, filters with very small pore size are utilized in order to trap the majority of particulates. However, flow velocity is limited, and flow volume, in order to be large, is associated with very large filter surface area.
However, in many environments, mere trapping of particulates is not enough. First, in some applications, particularly those involving infectious microorganisms, “zero tolerance” is the desired standard for viability of any microorganisms which may pass through filtration systems. Elimination of all particulates would involve filtration systems of such small pore size and hence large surface area that such filtration is not economically feasible. Second, the filters used in such applications must be disposed of in an environmentally responsive manner. For example, filters which may contain pathogens, toxins, or carcinogens must generally be incinerated at high temperatures.
Heated gas has been used to destroy gas-borne contaminants or to render pathogens non-viable. However, such systems employ external heat sources, i.e. heated tubes or ducts, internal resistance wire heating elements, or actual incineration in fuel-fed flames, which is obviously impractical for many uses. Tubes containing heated filaments of resistance wire have the drawback that the temperature must be kept very high, particularly at high gas velocities, since impingement of particles directly onto a heated filament is no more than a random event, and many particulates can otherwise pass through such devices without experiencing a high enough temperature for deactivation. Such systems also do not trap particulates to any substantial degree, and thus must be combined with filter elements for these purposes.
Numerous filtration media have been developed over the years, including porous and optionally chemically treated paper; fiberglass, including fiberglass coated with bioactive metals such as silver; microporous polymer films, for example those of nylon and polysulfone; open celled polymeric foams; sintered metals, ceramics, and glass, e.g. glass “frits,” and foamed metals and ceramics.
It would be desirable to provide a filtration system which is capable of rendering pathogenic particulates non-viable in addition to providing filtration per se. It would further be desirable to provide a filtration system where the flow rate can be maintained at high values. It would be yet further desirable to provide a filtration system which is regenerable, i.e. which does not rely on disposable filter elements.